1. Field of the Invention
The invention lies in the field of processing piece good concerns an installation according to the generic term of the first independent claim. The installation according to the invention serves the processing of flat objects, in particular of printed products, e.g. the packing of individual printed products or small groups thereof.
2. Description of Related Art
For many different kinds of processing such as e.g. binding, trimming, labelling, packing, etc., printed products are conveyed in conveying streams into a processing station and away from it. In such conveying streams the printed products lie, for example, on a conveying surface, such that they are arranged essentially parallel to the conveying direction. Advantageously the processing station is equipped in such a way that conveyance of the printed products need not be interrupted during processing but can be operated continuously. This implies that tools which have to act on the printed products during a predetermined time must be conveyed together with the printed product for the predetermined time, such that there is no relative speed with regard to the products, at least in the conveying direction.
If, for the processing the printed products in such conveying streams, only product edges need to be accessible, the printed products are usually arranged overlapping each other (imbricated stream). Therein the size of the accessible product part depends on product spacing (distance between imbricated products, i.e. distance between, for example, downstream edges of successive products). The accessible part of the product does not depend on the format of the printed product, as such. The product spacing is therefore adjusted to the nature of processing and can be maintained even if the format changes.
If the entire surface of the products must be accessible for the processing of printed products in conveying streams in which the products are arranged parallel to the conveying direction, the printed products are to be arranged consecutively on the conveying surface, without overlapping. For such conveyance the format of the product, i.e. their expansion in conveying direction, becomes relevant for the product spacing (distance between, for example, downstream edges of successive products). If diverse product formats are to be conveyed and processed in such a conveying stream without corresponding adjusting measures, the product spacing has to be adjusted to the largest format to be processed, i.e. the greatest product length to be expected in conveying direction. The product spacing (distance between, for example, downstream edges of successive products) then does not change and the gaps between products (distance between trailing edge of a product and downstream edge of the following product) are smallest for the largest products and greater for all the other products, depending on format. Conveyance of unnecessarily large gaps, which implies unnecessarily high conveying speed to achieve equal conveying capacity, is nevertheless an economical disadvantage.
This economical disadvantage becomes particularly relevant if it does not only concern the conveying speed but also the use of material for the processing. This applies to the use of an auxiliary material that is continuously supplied to the conveying stream and spans across the products and the gaps. For economical or other reasons such material ought to be limited to the amount required by a specific format.
A typical example of processing flat objects in a conveying stream using an auxiliary material, which is continuously supplied to the conveying stream, is the packing of objects with the aid of a packing material such as a plastic foil supplied from a reel. Therein it would be desirable, for economical reasons as indicated above as well as for other reasons (e.g. stability and aesthetic appearance of the packaging), to adjust the length of the supplied packing material for each object to be packed as precisely as possible to the size (format) of the object.
Publication EP-0588764 discloses an installation in which printed products, which are conveyed essentially at right angles to the conveying direction, are packed during continuous conveyance using a packing material supplied from a roll. The installation is a drum with radial conveying compartments, open at the drum periphery. The packing material is drawn from the roll and is continuously pulled to the bottom of each conveying compartment, thus forming a V-shaped pocket in each conveying compartment by zigzagging from compartment to compartment. The printed products to be packed are positioned in these pockets, the packing material is severed between the conveying compartments and the severed piece of packing material is sealed around the printed product in each compartment. The appropriate tools for drawing in, severing and sealing the packing material are provided in each conveying compartment. Obviously, objects of varying formats can be packed in this installation, but the size of the piece of packing material severed for each package is always the same and only depends on the size of the conveying compartment.
The installation described in the publication WO-00/64738 in essence serves the same purpose as the installation according to EP-0588764 and likewise comprises a processing drum, wherein the objects to be packed are conveyed consecutively and parallel to the conveying direction around a part of the drum periphery, together with the packing material. Tools for transverse sealing and severing of the packing material are arranged at this drum periphery and they move around this periphery together with the objects to be packed and the packing material. In this installation too, objects of varying sizes can be packed, but here too, the format of the packaging remains the same.
If single printed products or groups of printed products of a single format but varying thickness are to be packed in the aforementioned installations, it is already no longer possible to produce packages using only a minimum of the packing material by fitting it tightly around the printed products, because a thicker product requires, parallel to the conveying direction, a slightly longer piece of packing material. This applies in particular to printed product which are loosely folded, i.e. not bound, and therefore, in most cases not trimmed either (e.g. daily newspapers), such that their thickness has an effect on the breadth of the folding edge and therefore on the product expansion in conveying direction also. If variations of thickness have to be reckoned with, the installations must be adjusted to products having the largest thickness to be expected. For all thinner products the packaging material does not fit tightly around the product and is larger than absolutely necessary.
The same applies if varying packing materials necessitating varying seam widths are to be processed, or if the transverse seams are to be performed in varying ways requiring a web of packing material of greater or lesser width.
In the publications DE-3528634, U.S. Pat. No. 4,305,240 or GB-1409077 installations are described in which, again by means of drum-like installations, a continuous packing material is sealed at right angles by welding jaws arranged on the drum periphery. In order to achieve varying distances between the transverse seams, it is suggested that the welding jaws are arranged in a radially adjustable manner. With these installations, objects of varying sizes and/or varying gaps between objects can be sealed into a continuous packing material in the manner described above. However, as the processing drum comprises various diameters, depending on the radial adjustment of the welding jaws, it is necessary for the packing material to be of sufficient firmness in order to convey itself and the objects to be packed without further support across a last stretch of the path on to the drum periphery and/or across a first stretch of the path away off the drum periphery. Therefore, these installations can not be used for packing material unable to fulfil such conditions due to insufficient stability, and they are not at all suitable for processing methods which do not require a continuously supplied auxiliary material.